A diaphragm pump of the class with which the present invention is concerned generally includes a pumping section traversed by a secondary fluid medium to be delivered from one location to another and a working section charged with a primary working fluid medium, the pumping section and the working section being coupled by means of a connecting fitting through which the primary working fluid medium flows. A diaphragm of elastomeric material is adapted to be pulsatingly acted on by the working fluid medium and defines a part of the boundary of a pump chamber in the pumping section. The associated device for regulating the pressure and feed volume of the pump includes outlet and overpressure valves controlled by the primary working fluid medium in the working section of the pump for the admission and discharge of primary working fluid medium from and into a reservoir. The pump further includes a pressure regulating valve, an expansion chamber and a leakage bore-equipped nozzle for discharging into the reservoir any portion of the primary working fluid medium from the portion of the regulating device separated by the overpressure valves from the working section of the pump.
In a known regulating device of this type, such as is disclosed, for example, in German OLS No. 31 21 103, the portion of the primary working fluid medium which during the pressure phase is lost by being discharged through the nozzle into the reservoir, serves the purpose that during the following suction phase of the involved working section of the pump reduction in the quantity of primary working fluid medium in the working section creates an underpressure condition by means of which a secure engagement between the tubular diaphragm and its supporting pipe is achieved before, as a consequence of the existing underpressure condition in the system, the suction valve is opened for compensating for the missing primary working fluid medium. Although the known regulating device fulfills the objective of a loss-free control of the pressure and feed volume of the secondary fluid medium being transported, it suffers from a number of drawbacks and disadvantages. One of these is that during the suction stroke the end position of the diaphragm must be mechanically effected and transmitted to the valve actuated by the diaphragm. This requires special measures to be taken in regard to the construction of the regulating device, which not only makes the device more expensive but could also adversely influence the operational reliability of the diaphragm pump. Another disadvantage is that the regulating valve which is controlled by the pressure of the secondary fluid medium being transported is directly connected with the pressure expansion chamber, so that the control piston or diaphragm of the latter could possibly come into direct contact with the abrasive or chemically corrosive fluid medium being transported. The regulating valve thus is subjected to high mechanical and/or chemical demands and thus could constitute a point of weakness in the overall system. In the event of leakage at the regulating valve, furthermore, the secondary fluid medium could get into the flow system of and contaminate the primary working fluid medium, which under certain conditions could lead to the diaphragm pump being damaged or destroyed.